This invention relates in general to fault protection and, more particularly, to over-current protection of a motor driver.
Servomotors have many uses. They are useful for precisely controlling movement in a variety of circumstances. Servomotors are usually controlled by a driver circuit. The driver circuit provides current to the servomotor, which causes the motor to turn.
When a servomotor fails, it often presents a very low impedance to the driver circuit for the motor. Low impedance causes excessive current to flow through the driver circuit. Usually this excessive current causes a failure in the driver circuit.
Conventionally, high current protection is accomplished by fuses. Unfortunately, the when a servomotor fails, the current spikes so quickly in the driver circuit that fuses cannot react fast enough to protect the driver circuit.
According to principles of the present invention, a motor driver high current protector includes a voltage source, a current sensor, a comparator, a switch, a delay circuit, and an inhibitor. The current sensor is configured to sense current passing through the motor driver and output a voltage responsive to the sensed current. The comparator has an output and is configured to generate a low voltage at its output while the output of the current sensor exceeds a first reference voltage. The switch has an input, an output, and a base. The switch is activated by a low voltage at the output of the comparator and the base of the switch to close the switch. Closing the switch provides electrical communication between the input and the output of the switch. The input of the switch is connected to the voltage source. The delay circuit is connected to the output of the switch and is configured to decay the voltage at the output of the switch while the switch is open. The inhibitor is configured to inhibit the motor driver while the output of the switch exceeds a second reference voltage.
According to further principles of the present invention, the current sensor may be a resistor connected to the motor driver to sense the current passing through the motor driver and produce a voltage drop as the output of the current sensor.
According to further principles of the present invention, the switch may include first and second resistors for biasing the voltage at the base of the transistor. The first resistor is provided between the output of the comparator and the base of the transistor. The second resistor is provided between the voltage source and the base of the transistor.
According to further principles of the present invention, the inhibitor may include first and second inhibitor comparators, each of the inhibitor comparators has an output. Each of the first and second inhibitor comparators is configured to generate a low voltage at its output while the output of the switch exceeds a second reference voltage.